10) There are 2 $5 bills and 10 $10 bills.
Given: number of bills = 12
number of $5 = x
number of $10 = 5x
x + 5x = 12
6x = 12
6x/6 = 12/6
x = 2 number of $5 bills. ; no. of $10 = 5x = 5(2) = 10 bills.
11) Hillary and 23 friends = 24 total
girls = x
boys = x + 8
girls + boys = 24
x + x + 8 = 24
2x + 8 = 24
2x = 24-8
2x = 16
2x/2 = 16/2
x = 8 number of girls ; no. of boys = x + 8 ⇒ 8 + 8 = 16
12) total no. of miles = 248
miles drove in the morning = x - 70
miles drove in the afternoon = x
x + x - 70 = 248
2x -70 = 248
2x = 248 + 70
2x = 318
2x/2 = 318/2
x = 159 miles. *driven in the afternoon.
driven in the afternoon : x - 70 = 159 - 70 = 89 miles driven in the morning